Noise dose is computed using Table G-16a as follows:
When the sound level, L, is constant over the entire work shift, the noise dose, D, in percent, is given by: D=100 C/T where C is the total length of the work day, in hours, and T is the reference duration corresponding to the measured sound level, L, as given in Table G-16a or by the formula shown as a footnote to that table
When the workshift noise exposure is composed of two or more periods of noise at different levels, the total noise dose over the work day is given by:
D = 100 (C(1)/T(1) + C(2)/T(2) + ... + C(n)/T(n)),
where C(n) indicates the total time of exposure at a specific noise level, and T(n) indicates the reference duration for that level as given by Table G-16a
The eight-hour time-weighted average sound level (TWA), in decibels, may be computed from the dose, in percent, by means of the formula: TWA = 16.61 log(10) (D/100) + 90. For an eight-hour workshift with the noise level constant over the entire shift, the TWA is equal to the measured sound level
A table relating dose and TWA is given in Section II.
TABLE G-16A
A-weighted sound level, L (decibel)
Reference duration, T (hour)
80
32
81
27.9
82
24.3
83
21.1
84
18.4
85
16
86
13.9
87
12.1
88
10.6
89
9.2
90
8
91
7.0
92
6.1
93
5.3
94
4.6
95
4
96
3.5
97
3.0
98
2.6
99
2.3
100
2
101
1.7
102
1.5
103
1.3
104
1.1
105
1
106
0.87
107
0.76
108
0.66
109
0.57
110
0.5
111
0.44
112
0.38
113
0.33
114
0.29
115
0.25
116
0.22
117
0.19
118
0.16
119
0.14
120
0.125
121
0.11
122
0.095
123
0.082
124
0.072
125
0.063
126
0.054
127
0.047
128
0.041
129
0.036
130
0.031
In the above table the reference duration, T, is computed bywhere L is the measured A-weighted sound level.
Conversion Between "Dose" and "8-Hour Time-Weighted Average"
Sound Level
Compliance with paragraphs (c)-(r) of this regulation is determined by the amount of exposure to noise in the workplace. The amount of such exposure is usually measured with an audiodosimeter which gives a readout in terms of "dose." In order to better understand the requirements of the amendment, dosimeter readings can be converted to an "8-hour time-weighted average sound level." (TWA).
In order to convert the reading of a dosimeter into TWA, see Table A-1, below. This table applies to dosimeters that are set by the manufacturer to calculate dose or percent exposure according to the relationships in Table G-16a. So, for example, a dose of 91 percent over an eight hour day results in a TWA of 89.3 dB, and, a dose of 50 percent corresponds to a TWA of 85 dB
If the dose as read on the dosimeter is less than or greater than the values found in Table A-1, the TWA may be calculated by using the formula: TWA = 16.61 log(10) (D/100) + 90 where TWA=8-hour time-weighted average sound level and D = accumulated dose in percent exposure.
TABLE A-1 - CONVERSION FROM "PERCENT NOISE EXPOSURE"
OR "DOSE" TO "8-HOUR TIME-WEIGHTED
AVERAGE SOUND LEVEL" (TWA)
